Various presensitized plate for use in making a lithographic printing plates requiring no fountain solution (hereinafter referred to as "waterless lithographic printing plate") for lithographic printing without using fountain solution have been proposed. Above all, those disclosed in JP-B-54-26923 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), JP-B-55-22781, JP-B-56-23150 and JP-A-2-236550 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application") comprising a primer layer, a photosensitive layer and a silicone rubber layer formed in this order on a support have extremely high performances.
These silicone rubber layers used for waterless lithographic printing plate function as an ink-repellent layer and, in general, high polymers comprising polysiloxane as a main skeleton partially crosslinked by a crosslinking agent are used as silicone rubber layers. In general, the following two methods are used as the curing method of silicone rubber layers:
(1) Condensation type: a method of making silicone rubber by crosslinking polysiloxane having hydroxyl groups at both terminals with silane or siloxane having a hydrolyzable functional group directly bonded to a silicon atom.
(2) Addition type: a method of making silicone rubber by addition reacting polysiloxane having an .tbd.SiH group with polysiloxane having a --CH.dbd.CH-- group (these methods are disclosed in JP-A-61-73156, JP-A-2-226246, JP-A-2-236550, JP-A-3-161753, JP-A-4-68353, JP-A-4-174437, JP-A-6-83045 and JP-A-4-239576).
The condensation type silicone rubbers in the above (1) have a disadvantage in that the curability thereof and adhesion to the photosensitive layer fluctuate according to the water content in the atmosphere during curing and as a result, when the condensation type silicone rubbers are used for the preparation of the waterless lithographic printing plates, it is difficult to produce the printing plates stably due to the fluctuation of sensitivity. Accordingly, the addition type silicone rubbers in (2) above having no such a drawback are thought to be superior.
These waterless lithographic printing plates are very liable to be scratched because the surface layer is a silicone rubber layer and they must be handled very carefully after development compared with the general lithographic printing plate comprising the photosensitive layer formed on an aluminum support. When the silicone rubber layer is scratched, the scratch can be retouched by coating a correction liquid if it is a non-image area, but plate making must be made over again if an image area is scratched. Further, waterless lithographic printing plates have a drawback of being inferior in impression capacity compared with the general lithographic printing plates. For example, the plate surface is scratched during printing or the adhesion between the silicone rubber layer and the photosensitive layer is not sufficient and the silicone rubber layer peels off partially during printing leading to printing failure, and an improvement has been accordingly strongly desired.